1. Field of the Invention
This invention relates to an display apparatus for projecting an image displayed on a cathode ray tube, and more particularly relates to improvement of a display apparatus having a structure for cooling a cathode ray tube with cooling liquid.
2. Description of Related Art
Recently, with popularization of multi-media apparatuses and computers, demand for a display apparatus having a large screen has risen increasingly. Various types of television receivers, image monitors, and image projectors which use a cathode ray tube (CRT) have been proposed as display apparatuses for displaying images of this sort. Among these display apparatuses, a type of display apparatus having structure for enlarging an image displayed on a cathode ray tube and displaying the enlarged image on a screen has been known. A display apparatus of this type can project the light of an image onto the front side of the screen or display an enlarged image on the screen by projecting the light of the image from the back side of the screen.
A projection type display apparatus for forming an image by projection is provided with three cathode ray tubes corresponding to a red (R) image, a green (G) image, and a blue (B) image to be projected on the screen side. These images displayed by these cathode ray tubes are subjected to optical processing through lenses and projected on the screen side. Because the respective cathode ray tubes generate heat, the cathode ray tubes should be cooled with cooling liquid. Cooling liquid used for cooling a cathode ray tube is usually a liquid mixture which is non-volatile under a normal temperature containing mainly, for example, ethylereglycol, and such cooling liquid is apt to stay without evaporation.
FIG. 1 shows a conventional projection type display apparatus. This display apparatus has three cathode ray tubes 1000, 1001, and 1002; the respective cathode ray tubes 1000, 1001, and 1002 form images of monochromatic colors namely red (R), green (G), and blue (B), and the respective images are projected on the screen 1004 through lenses 1003 to form a color image on the screen 1004. Cooling mechanisms 1005 for holding cooling liquid are provided between these cathode ray tubes 1000, 1001, and 1002 and corresponding lenses 1003.
FIG. 2 shows a cathode ray tube 1000 (1001, and 1002) and the cooling mechanism 1005. The cooling mechanism 1005 has a metal box 1006, and a metal box 1006 has the structure for containing cooling liquid 1007 in the metal box 1006. Cooling liquid 1007 is charged from a hole 1008, and a sealing screw 1009 is tightened after charging so that the cooling liquid 1007 does not leak through the hole 1008.
FIG. 3 and FIG. 4 show a screw 1009 tightened in the hole 1008 of the metal box 1006. An O-ring 1011 for sealing is provided between the screw 1009 and the groove 1010 of the metal box 1006.
Application of such structure causes problems as described hereafter. In FIG. 2, when cooling liquid 1007 is charged into the metal box 1006 though the hole 1008 and thereafter the screw 1009 is screwed into the hole 1008, as shown in FIG. 4, a part 1007A of the cooling liquid 1007 is confined in a space defined by the groove 1010, the O-ring 1011, and the screw 1009, because cooling liquid remains in the groove 1010 when cooling liquid is charged.
The needless liquid 1007A confined as described herein above leaks slowly with time to the outside from the space defined by the screw 1009, the groove 1010, and the O-ring 1011. Thus cooling liquid 1007A leaks though there is no structural defect and fabrication defect. The cooling liquid which leaks to the outside remains on the metal box 1006 because cooling liquid is non-volatile under a normal temperature.
It is an object of the present invention to provide a display apparatus having a structure for discharging and removing needless cooling liquid consistently when a display apparatus having a structure for cooling a cathode ray tube with cooling liquid is fabricated.
The present invention is accomplished by using a display apparatus having a structure for projecting and displaying an image displayed on a cathode ray tube and having a structure for cooling the cathode ray tube with cooling liquid provided with a cooling liquid container for containing cooling liquid for cooling the cathode ray tube, a sealing member for sealing cooling liquid in the cooling liquid container by plugging a cooling liquid charging hole formed on the cooling liquid container after cooling liquid is charged into the cooling liquid container, and a residual cooling liquid discharge outlet provided with connection to the sealing member and the cooling liquid container for discharging residual cooling liquid in the space between the sealing member and the cooling liquid container to the outside through the space between the sealing member and the cooling liquid container.
In the present invention, the cooling liquid container contains cooling liquid used for cooling a cathode ray tube. The sealing member seals cooling liquid in the cooling liquid container by plugging the cooling liquid charging hole formed on the cooling liquid container after charging of cooling liquid into the cooling liquid container. The residual cooling liquid discharging outlet provided with connection to the sealing member and the cooling liquid container functions to discharge and remove residual cooling liquid remaining in the space between the sealing member and the cooling liquid container to the outside though the space between the sealing member and the cooling liquid container. Thereby, residual cooling liquid remaining in the space between the sealing member and the cooling liquid container is discharged to the outside easily through the cooling liquid discharge outlet, the problem of confined cooling liquid is solved, and liquid leakage is eliminated.